The present disclosure relates to tin snips. More particularly, the invention relates to tin snips having a two-stage force multiplier capable of changing the mechanical advantage.
Snips or shears are among the most commonly used hand tools in industries ranging from sheet metal formation to gardening. Conventional snips or shears generally comprise an upper and lower cutting blade, each having elongated handles extending therefrom and attached thereto. The cutting blades are configured to pivot around a single axis point that separates the cutting blades from the handles. The cutting motion is activated by applying a constant force to the exterior of the handles. This exterior force effectively closes the handles. Correspondingly, the cutting blades close around the single axis point and engage an object to be cut at a variable point along the edges of the cutting blades. The force generated at the point of contact between the material being cut and cutting blades is essentially constant throughout the cutting stroke as the cutting blades are configured to pivot around the single axis point.
Mechanical advantage, or the factor by which the force output (i.e. force exerted at the point of contact between the cutting blade and material) is measured relative to the force input (i.e. force exerted on the handles), is largely important when considering that tin snips and cutting shears have a large range of applications. Accordingly, with a large range of applications comes an equally large range of cutting effort depending on the specific application. For example, cutting force varies in the sheet metal forming industry depending on the type of sheet metal, sheet metal thickness, and sheet metal material composition. When using snips as shrubbery shears, the thickness, durability, and variety of vegetation all determine the required cutting force.
For conventional snips or shears having a single point of rotation, the mechanical advantage consists of a relatively straight-forward computation. To illustrate the mechanical advantage of conventional snips or shears, consider the following unit-less calculation: torque (T)=force (F) distance (D). In conventional tin snips, an input force is applied to the handles of the tin snips via a user's hand and thereafter an output force is generated at the point of resistance—i.e. the contact point between the cutting blades and material being cut. The distance from the above-equation is measured from the input/output force points to the single axis point separating the handles and cutting blades. Respective torque equations for the handles and the cutting blades would equal: T (handles)=F (input)*D (input) and T (cutting blades)=F (output)*D (output). Accordingly, under the abovementioned principle, T (handles)=T (cutting blades). Thus: F (input)*D (input)=F (output)*D (output). While conventional snips or shears may widely vary in size and shape—consider for this example that the distance between the input force point on the handles and the single axis point is 5× longer than the distance between the output force at the point of cutting blade and material contact and the single axis point. Therefore: D (input)=5D (output). The equation is thus rearranged to solve for the output force: F (output)={[F (input)*5D (output)]/D (output)}. Therefore: F (output)=5F (input). Here, a user can exert an output force on an object to be cut that is 5× the input force. In this example, the mechanical advantage is largely generated by the difference in the distance D (input) of the handle relative to the distance D (output) of the cutting blades. Mechanical advantage is important because it enables users to exert higher cutting forces on objects, forces that may otherwise be unobtainable.
A person employing use of the conventional snips or shears having a single axis point, as in the above example, will require a variety of tools designed for each specific cutting assignment. Tools with longer handles will be employed for assignments requiring larger output force, while smaller tools having shorter handles will be employed for assignments requiring less output force. Even so, snips or shears intended to cut harder materials may require unacceptably large amounts of physical input force. Or, alternatively, operation of large tools may become overly cumbersome and inoperable due to the long and bulky handle size.
Thus, there exists a significant need for improved tin snips having increased, variable mechanical advantage. Such improved tin snips should include a two-stage compound mechanism having a sliding adjustment pivot point. The mechanical advantage of the tin snips increases by creating extra handle leverage when sliding the adjustment pivot point from a first compact position to a second extended position. Such improved tin snips may also include a mechanism for inverting the handles to provide a compact and mobile design. The present invention fulfills these needs and provides further related advantages.